What Causes Headaches And Twitching In Eyelid?

My eyelid has been twitching for about four weeks. It is the bottom lid on the right eye. It is not all day, but it twitches several times a day some days more often than others. Today has been pretty often and pretty severe. After about two weeks I began occasionally also having headaches around the same time. I am not sure if they are related. I have read that it could be caused by stress and tiredness but I don't think I am suffering from either (I say think because I have had stress issues in the past that I did not realize were bad until I began having headaches). My question is how concerned should I be and how long should I allow them to continue before being concerned.